if IE6 open localhost:3000 , the result is "ie6"
if IE9 open localhost:3000 , the result is "ie9"
if Chrome open localhost:3000 , the result is "chrome"
if Opera open localhost:3000 , the result is "opera"
if Safari open localhost:3000 , the result is "safari"
if Firefox open localhost:3000 , the result is "firefox"
if Maxthon open localhost:3000 , the result is "chrome"